Browsing by Author "Gibson, Sam J."

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    Absolute angle measurement using dual-wavelength laser speckle: theory and method
    (Elsevier, 2023-11-30) Gibson, Sam J.; Charrett, Thomas O. H.; Tatam, Ralph P.
    This paper presents a method utilising the speckle pattern formed by dual-wavelength illumination for the measurement of the two out-of-plane surface angles with respect to the sensor frame. Theoretical expressions are derived relating the observed speckle shift between patterns formed by two wavelengths for tilted surfaces with both on-axis and off-axis detector positions. These expressions are verified experimentally, showing RMS errors of between 0.5–1.0 . Finally, an on-axis implementation of the concept is presented using dual-wavelength illumination generated from two modes of a standard FP diode laser. Simplified expressions for the calculation of surface angles from measured speckle shift using this arrangement are presented, given in terms of three sensor constants; the responsivity or sensitivity of the sensor, C, and the zero surface tilt speckle shifts, Ax0 and Ay0. Experimental results using this sensor for a range of surface tilts between 0.0° and 7.5° showed an RMS error of 0.10° in θx and 0.19° in θy.
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    Towards high resolution absolute angle sensing using dual-wavelength laser speckle
    (IEEE, 2024-06-28) Gibson, Sam J.; Charrett, Thomas O. H.; Tatum, Ralph P.
    We present a two dimensional angle sensor with greater than 0.01 degrees resolution, using dual-wavelength laser speckle. The technique uses speckle correlation of a double speckle pattern, determining absolute surface tilt from a single frame. A constructed sensor was used to measure a grid of 2D angles between ±0.25° rotating around both x and y axes. Sensor performance was limited by laser mode instability effects, however an analysis of measurements demonstrated that a stable mode output could achieve bias errors of less than 0.010°, and standard deviations of 0.003° around x and 0.021° around y .